Objectives: The continuing major objective of this project is to perform comparative studies of neoplasia in invertebrate and lower vertebrate animals. Such studies serve two main needs: 1) To gain a comprehensive view of the biology of neoplasia throughout the animal phyla and thus to achieve a more detached perspective of the problem of cancer in man; 2) To find and make use of neoplastic diseases in lower animals in 2 ways; a) by adapting them to experimental uses in studies of the properties and mechanisms of genesis of cancer, b) by using them as indicators of environmental tumorigenic agents possibly related to the epidemiology of human neoplasia. Major findings: A culture cell line from a nephroblastoma in a rainbow trout has been isolated and maintained for 1 year. The line grows slowly at room temperature and can be subcultured at intervals of 1-2 months. The original spontaneous tumor, like several others we have seen in rainbow trout, was well-differentiated showing only slightly atypical glomerulus and tubule formation. In culture, cells show epithelial as well as mesenchymal characteristics. During the past year, this cell line was placed in contact co-culture with dorsal spinal cord from 11-day mouse embryos, to see whether the nephroblastoma cells might be capable of tubulogenesis under this stimulation. There was no response of any type on the part of the nephroblastoma cells. Only a single set of cultures was studied, but excellent contact was established between spinal cord and masses of the cultured cells, and the result was unequivocally negative. Proposed course: 1. The field search for cholangiomas in suckers will be continued. 2. The collaborative histopathologic study of gonadal tumors in carp will be extended until a satisfactory histogenetic classification can be accomplished.